Boron Nitride (BN) occurs in both cubic and hexagonal crystalline form. The two forms exhibit quite different properties associated with the structural difference. Cubic boron nitride is the second hardest material known. Hexagonal boron nitride (hBN) is readily machinable.
The structure of hBN is discussed in Edgar, Properties of Group III Nitrides, Chapter 1, p. 8. According to Edgar, hBN is a layered structure, closely analogous to graphite. In hBN the layers are stacked in perfect registration where the hexagonal rings in all layers coincide. However, the positions of N and B alternate from layer to layer, resulting in the structure depicted in FIG. 1. According to Edgar, the B—N bond length within the layers is much shorter (0.1446 nm) than the B—N bond length between layers (0.33306 nm).
Phaal et al., U.S. Pat. No. 4,008,055, prepared nickel coated cubic boron nitride needles that were incorporated into a resin base and oriented in a magnetic field to form an abrasive tool.
Caveney et al., South African Patent Application 704346, discloses an epitaxial coating of Ni, Fe, or Co adjacent to the surface of a cubic BN particle for use in forming an abrasive tool.
Li et al., Metallurgical and Materials Transactions, B, 38B, 149ff, (2007), discloses the surface coating of hBN particles with a dense coating of Ni.
Dennis et al., Brazilian Patent Application (11)(21)7501169 discloses the growth of epitaxial titanium boride crystals on the surface of cubic BN particles.
Vladimir et al., Czechoslovak Patent 243893, disclose a process for preparing hBN particles with epitaxial Ni on the surface of the particles thereof.